This week on Car Talk, Maria's car was minding its own business in her boyfriend's driveway, until his ex-wife came along and gave it a tap, which sent it rolling straight on down to the Connecticut River. Was the ex's tap more of a shove, or is Maria's boyfriend guilty of leaving it in "ready to roll" position? Elsewhere, Debra's truck is making a mysterious knocking sound; Matt's wife won't go near their new car after a mouse spotting; and Sara's got the DIY bug, and wants to tackle a transmission rebuild. Also, on Stump the Chumps, did Tom and Ray help dog-trainer Vicky choose the right pet-mobile? All this, and lots more, this week on Car Talk.